Nitrate salts, such as ammonium nitrate (“AN”), has been used as both a liquid-water solution and as solid particles (e.g. prills) in the fertilizer and explosives industry. Ammonium nitrate is made from anhydrous ammonia and nitric acid, which is also synthesized from ammonia, and is produced in forms ranging from liquid solutions, to crystals, to porous, multi-crystalline agglomerates. Such compounds include granules and prills. These compounds generally have coatings applied thereto after the granule or prill is formed to prevent caking and clumping. Such compounds have also been developed which include internal additives used during the granulating or prilling process to produce a high-quality salts. Solid forms of nitrate salts encountered in industry include high density prills (low porosity) and granules, which are made by a granulation process.
Typical external coatings for nitrate compounds can be binary, i.e., two distinct materials, that act synergistically in their function physically and/or chemically. For example, an organic surfactant can be used to help clay or talc adhere to the nitrate compound and/or also contribute to anti-caking properties. Typically, the clay or talc acts as a “physical parting agent” and the surfactant acts chemically as an “anti-caking agent.” Both actions reduce caking and clumping of the nitrate compound. More common in the industry today, nitrate compound coatings are strictly organic in nature consisting of blends of such materials including: mineral oil, waxes, anionic and cationic surfactants. These mixtures provide both physical and chemical action to prevent caking. Caking and clumping of nitrate compounds before use is a common problem in industry and it occurs more frequently in the summer months during high humidity conditions.
Ammonium nitrate is the basis for almost all commercial explosives used in the world today. For example, water-in-oil emulsion explosive compositions are one of the prevalent commercial explosives. They are composite explosives that comprise an emulsified dispersion of a discontinuous phase of oxidizer salt solution droplets (comprising AN with possible another oxidizer salts) in a continuous organic fuel phase. This dispersion or emulsion phase is held in place (stabilized) by a water-in-oil emulsifier(s) system that largely prevents coalescence of the dispersed oxidizer phase. The inorganic oxidizer salt solution droplets are typically in a super-cooled state and thus want to crystallize, consequently destabilizing the emulsified state. Thus, if the emulsified state is weakened by stress, aging or emulsion poisons (materials that cause de-emulsification), the emulsion will manifest this by crystallization which desensitizes the emulsion explosive and can render it un-detonable.
Ammonium nitrate in solid particulate form, generally as prills typically 1-3 mm in diameter, is also widely used in admixtures with emulsion explosives. Explosives consisting of a water-in-oil emulsion and oxidizer salt prills, generally ammonium nitrate prills, are known as “blended explosives” and have a high bulk density, good blasting energy and can have good water resistance depending on the ratio of emulsion to AN or ANFO (ammonium nitrate/fuel oil mixture) in the blend. However, disadvantages involved in the use of blended explosives having particulate oxidizer salt relate to the blend's pumpability and stability. More importantly, the blend's stability relates directly to the explosive properties of the blend. Further, some blends must be-processed, loaded, and detonated expeditiously after blending because over a short period of time the emulsion destabilizes (“breaks”) and becomes hard, thus making the blend unpumpable and even undetonable. This can be especially true for blended emulsions using prills or other solid forms having certain internal additives and/or coatings which can act to destabilize the emulsion component of the blend.
In many places in the developed world, AN solution has been available directly from manufacturing plants. This “virgin liquor” gives the optimum stability to emulsion products. However, as blasting operations spread to more remote regions, far from AN plants, the necessity of using solution made from dissolving AN compounds to blend emulsion explosives is rapidly increasing.